This invention pertains to an AC-to-DC converter circuit, and in particular, to such a circuit which employs a bridge rectifier featuring legs containing insulated-gate bipolar transistor (IGBT) switching/rectifying devices.
The converter of the present invention, in relation to the structure and operation of the mentioned bridge rectifier, is a very simple and economical structure, with respect to which the choice to employ IGBT devices in two of the legs in the bridge circuit results in significantly improved efficiency in operation over prior art converter circuits, and related, normal operation and with only modest heat loss. Cooperating with the bridge rectifier in the overall converter circuit is a zero-crossing tracker which collaborates with a flip-flop device to trigger operations of the IGBT devices. Preferably, such triggering taking place through opto-isolator structure. The specific design and disposition of the zero-crossing tracker and cooperating flip-flop in this invention is such that if, for some reason, the tracker fails in its operation, the overall operation of the bridge rectifier, and thus effectively of the converter as a whole, shuts down so as to remove, effectively, any DC output voltage. Additionally, the zero-crossing tracker, during normal operation, coacts with the mentioned flip-flop circuit, and with firing of the IGBT devices, to play a role in effecting reliable output voltage-level control.
Use, in accordance with this invention, of IGBT switching/rectifying devices in the bridge rectifier is to be distinguished from conventional use in converter rectifier circuits of so-called SCR devices. As is well known, an SCR device cannot be switched arbitrarily from a conducting state, and specifically cannot be turned off selectively with anything approaching the versatility and timing precision of the turn-on and turn-off operations that characterize the behavior of an IGBT device. In addition, IGBT devices are faster switching devices than are SCRs. As a consequence, conventional SCR rectifiers cannot be employed to create an AC-to-DC converter which has the remarkable flexibility and operation of the circuit of the present invention. Further, the xe2x80x9conxe2x80x9d resistance to current flow in an IGBT device is extremely low, and specifically, much lower than that which is characteristic of an SCR device. Accordingly, an IGBT device turns out to be inherently a better-efficiency device, one requiring less energy to turn on, and one which generates less dissipatable heat during normal use.
All of these important advantages that are offered by use, according to this invention, of IGBT rectifying/switching devices, result in an overall structure wherein efficiency of operation, simplicity of packaging, and minimization of heat dissipation, are dramatically improved over the prior art offerings.
Various other objects and advantages that are attained by this invention will become more fully apparent as the description which now follows is read in conjunction with the accompanying drawings.